1. Field of the Invention
The present invention relates to a micro air delivery device, and more specifically, a micro air delivery device capable of actively supplying a certain amount of air to a predetermined space in a valveless structure.
2. Description of the Related Art
Generally, a micro air delivery device is used for supplying a certain amount of air to a small electronic machine or a part. There has been an increase in demand for a micro air delivery device as the use of portable electronic devices such as laptop computers, PDAs, and mobile phones has become popular, especially for fuel cells used in such portable electronic devices. Further, micro air delivery devices are required in supplying appropriate amounts of air to critical parts of computers such as certain chips, or, more generally, for cooling parts by circulating air.
Small fuel cells employed in portable electronic devices such as conventional mobile phones or PDAs that use micro air delivery devices include the following: PAFC (Phosphoric Acid Fuel Cell), AFC (Alkaline Fuel Cell), PCMFC (Proton Exchange Membrane Fuel Cell), MCFC (Molten Carbonate Fuel Cell), SOFC (Solid Oxide Fuel Cell), and DMFC (Direct Methanol Fuel Cell), according to the type of fuel, running temperature, catalyst utilized and electrolyte employed.
An air delivery device used with a DMFC, which has recently shown substantial performance, will be explained as an example.
The DMFC generates electric power using methanol fuel and oxygen to cause a chemical reaction in an MEA (membrane and electrode assembly). The chemical reaction is described in detail as the following.
The DMFC comprises a membrane 15, an anode 16 and a cathode 17 which are disposed at both sides of the membrane 15, as shown in FIG. 1. In anode 16, the methanol and water react to generate a hydrogenous ion and an electron. The reaction formula is expressed in a [Reaction formula 1] as follows.CH3OH+H2O=CO2+6H++6e+  [Reaction formula 1]
In cathode 17, the hydrogen ion generated from anode 16 moves through membrane 15 and combines with oxygen to generate water. The reaction formula thereof is expressed in a [Reaction formula 2] as follows.1.5 O2+6H++6e−=3H2O  [Reaction formula 2]
The whole reaction formula in the fuel cell is expressed in a [Reaction formula 3] as follows.CH3OH+1.5 O2=CO2+2H2O, E0=1.18v  [Reaction formula 3]
As described above, the DMFC converts chemical energy generated through the whole chemical reaction to electric energy, and supplies it to an electronic device.
In such a chemical reaction, usually oxygen, one of the reactants, can be directly supplied from the surrounding air, and the methanol fuel cell is supplied by a natural air convection system or an active air supply system. For an active air supply system, a flow supplying apparatus such as a check valve-type pump or a MEMS-type pump can be used to supply a predetermined air or flow.
However, in most cases, a natural air convection system is employed for supplying air due to size limitations. In this situation, an orifice structure which is directly connected to the outside air is provided to supply air to the MEA.
FIG. 2 illustrates an air delivery device of a natural air convection system with the above structure. Such an air delivery device is disclosed in U.S. Pat. No. 6,497,975B2.
As shown in FIG. 2, the outside air is directly delivered to an MEA 20 through a plurality of orifices 25 formed in a main body 30. However, this type of micro air delivery device has several problems.
First, where the air delivery device is used with diverse electric devices such as mobile phones or the PDAs, a user usually holds the device by a hand. Therefore, orifice 25 which is an air path formed for the air delivery device, or a similarly situated cavity can be covered by the user's hand. As a result, air flow can become constricted. Further, orifice 25 can also be blocked by secretions from the hand.
Second, since the reaction in the MEA is exothermic, the surface temperature of the MEA is relatively high compared to the outside air temperature. Therefore, because of this temperature difference, it is unnatural for air to flow into and through orifice 25.
Third, it is hard to control the amount of air flow required. That is, with respect to different portable electronic devices, different degrees of power are required according to respective modes of use. Accordingly, different amounts of air flow are required for different devices. However, conventional air delivery devices are not able to control the flow of the air. In addition, the air delivery rate or flow for natural convection is comparatively low, and consequently, it is not adequate in generating electric power.